The proposed research project is designed to address two issues. The first objective is to describe the motor response of the diaphragm to mechanical or chemical stimulation. Secondly, experiments are also planned to characterize the response of single diaphragmatic afferents to similar stimuli. Project 1 is designed to assess the influence that sudden changes in the length of the diaphragm and inspiratory airway occlusion have on electromyograms (EMGs) from the costal and crural regions of the diaphragm. C-7 spinalized, bilaterally vagotomized cats will be studied while mounted in a spinal suspension frame. Three maneuvers will be used to alter diaphragmatic mechanics: rapid stretch of the diaphragm, inspiratory occlusion and sudden decrease of the length of the diaphragm. Sonomicrometry will be used to assess changes in the operating length of the diaphragm. Possible medullary involvement in the reflex response to the mechanical perturbations will be determined by recording the genioglossus (GG) EMG. As an additional test of medullary pathways, the quick stretch (balloon) experiments will be repeated in a C-1 cord transected preparation (artificially ventilated). A preparation involving isolation of the circulation of the left crus will be used in Project 2 for close intra-arterial perfusion of test chemicals. Each drug will be tested as to its local action as well as any effect noted on central respiratory drive before and after dorsal root transection. The site of central integration of this afferent activity elicited by each compound will also be determined. Project 3 is designed to characterize the response of diaphragmatic afferents to mechanical and chemical stimulation. Single unit recordings from muscle spindles, tendon organs and C-fibers will be made from uncut dorsal root filaments at the 5th and 6th cervical levels. In project 3A activity from an identified diaphragmatic receptor will be correlated to the resultant motor responses (EMG) elicited while the cat is exposed to the mechanical perturbations outlined in project 1. Project 3B is designed to characterize the response of diaphragmatic afferents associated with local infusion of the chemical agents shown in project 2 to be effective in altering respiratory motor drive. Projects 1, 2 and 3 will provide important basic information regarding autogenic reflex control of the diaphragm.